Nitrogen Lewis acids unveiled

Abstract

Lewis acids and bases are one of chemistry’s fundamental concepts, depicting a molecule’s ability to accept an electron pair from a partner molecule or to donate an electron pair to a partner, respectively. For example, electron-rich nitrogen-centered molecules such as ammonia function as Lewis bases. Mark Gandelman of Technion—Israel Institute of Technology and his group have found a situation in which they can turn that donor-acceptor reactivity around, so that a nitrogen-centered molecule functions as a Lewis acid (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.6b12360). Gandelman’s group had previously studied a triazolium salt and found it to be an analog of imidazole-based N-heterocyclic carbenes, including the ability to serve as a ligand for transition metals. The central nitrogen of the saturated N–N–N triazolium unit in the molecule can accept electron density from a metal into a vacant p orbital, even though it weakly donates its lone pair of electrons residing